1. Field of the Invention
The present invention relates generally to carboxylic acid production processes. More specifically, the present invention concerns equipment and processes for producing carboxylic acids employing solvent originating from a process involving esterification of lignocellulosic material.
2. Description of the Prior Art
In conventional terephthalic acid (“TPA”) production processes, para-xylene undergoes oxidation to form crude terephthalic acid (“CTA”) particles. A slurry of CTA particles can then undergo purification to form purified terephthalic acid (“PTA”) particles. A purified slurry comprising PTA particles and a liquid phase can then be treated in a product isolation zone to isolate at least a portion of the PTA particles. During the TPA production process, a solvent is typically introduced into the oxidizer along with the para-xylene. Additionally, solvent can be added during the purification step to replenish solvent lost during the oxidation process due to decarboxylation. This solvent initially acts as a carrier fluid for the para-xylene, and later as a carrier fluid for the TPA formed in the oxidation reactor. Though these processes are generally known in the art, given its high global demand improved production processes for TPA are continually needed.
In another process, lignocellulosic material (e.g., wood) can undergo esterification (e.g., acetylation) for purposes of, inter alia, making the lignocellulosic material more dimensionally stable, more weather resistant, and/or insect resistant. In a typical lignocellulosic material esterification process, the lignocellulosic material is contacted with a compound containing an acetyl group, such as acetic anhydride. The hydroxyl groups in the lignocellulosic material can then react with acetyl groups from the anhydride, thus forming acetylated lignocellulosic material and an acid-containing composition. When acetic anhydride is employed in this process, acetic acid is produced as a byproduct. A portion of the acetic acid can be recycled in order to form more anhydride by, for example, a cracking process and reaction with ketene. However, at least a portion of the acid can be removed from the process in order to control the level of impurities, such as, for example, terpenes.